The Deliberating Brain: Columbia’s Mind Brain Behavior Initiative

Not long ago, my editor asked if I wanted to cover a lecture
by a premier neuroscience researcher on the fascinating topic of “the
deliberating brain,” preceded by cocktails at one of New York’s most elegant
old hotels.

As decisions go, I thought, this was a no-brainer.

But I was wrong. One thing that Dana Alliance member Michael
N. Shadlen, M.D., Ph.D., made very clear in his talk, hosted by the Columbia
University Mind Brain Behavior Initiative
 and sponsored by the Dana
Foundation, is that no decision is a no-brainer. “By understanding the building
blocks of decision making,” he told his audience, “we can understand how the
brain achieves cognition writ large.”

Because complicated decisions—whom to choose as a life
partner or elect as president, whether to attend a lecture—are hard to study in
the lab, Dr. Shadlen and his colleagues devised simple tasks to illuminate
these building blocks. In his lecture, he summarized a series of experiments in
his laboratory, which he recently
moved from the University of Washington to Columbia, that showed how the brain
weighs evidence to choose between alternatives.

He and his colleagues taught monkeys to identify five
geometric shapes that supported the choice of “red,” five that suggested the
right choice would be “green.” But the evidence was weighted: some shapes provided
strong evidence in favor of their respective color, some weak, the same way
some cues in the environment are more reliable than others. After seeing a
sequence of four shapes, the animals chose one color or another, and were
rewarded if correct.

The researchers taught the monkeys to signal their choice by
moving their eyes toward a red or green spot, and placed an electrode to record
activity in a single neuron in the “association cortex,” a region between brain
areas that processes visual signals and those that direct eye movement. One
feature of association cortex neurons, Dr. Shadlen explained, is “persistent
activity”—the ability to keep firing while waiting to direct a response.

“Many of us feel that persistent activity holds the key to
higher brain functions in general, not just decision making. To achieve our most
cherished mental feats, the brain must use, represent, and compute with information
that is not tied to immediate change in the sensory world.” On this basic level,
he suggested, “cognition is an elaboration in evolution on a simpler brain that
delivered sensation to the motor system directly; as we got a bigger brain, we
were free from acting on information in the moment.”

In the videos that
followed, we in the audience were privileged to see—and hear—the deliberating
brain in action. A graph displayed the frequency of “spikes” of electrical impulses
from the neuron in question as the monkey saw a sequence of shapes, while the
audio played the crackle of electrical activity. In one trial, the line rose as
more evidence for “red” was presented, and the sound reached a crescendo. In
another, the electrical activity started out fast and loud, as the first shape
strongly supported red, but then dwindled dramatically as successive shapes
signaled green as the better choice.

“What we’re witnessing,” Dr. Shadlen said, “is a single
cell, in a single decision, adding and subtracting, accumulating evidence and
integrating it. We think this is the neural substrate for deliberating and
reasoning… the building blocks of decision making and cognition.”

“I’m a neurologist, and twenty years from now I’d like to
see the fruit of my labors make their way to the bedside”: these same building
blocks, he believes, are fundamental in disorders of higher brain function. While
the causes of schizophrenia, autism, and attention deficit disorder may prove
genetic or toxic, “in the end they will manifest in failures of things like
evidence accumulation, persistent activity, and the ability to know when to
stop deliberating.”

Drugs to restore these core functions, Dr. Shadlen predicted,
will come from an understanding of the brain in which his research will act in synergy
with the work of others investigating synapses, genes, and proteins. The potential
for such interdisciplinary progress, he said, “is why this decision maker chose
to leave the beautiful Pacific Northwest for the mud near the 125th
St. subway stop,” where the future home of Columbia’s Mind Brain Behavior Initiative
is under construction.

–Carl Sherman

Carl Sherman is a science writer in New York City.

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